feat: use official singularity image

This would remove the need to maintain a special dind image.

.gitlab-ci.yml

@@ -413,7 +413,7 @@ jug_xl:nightly:
 .singularity:
   image:
     name: ${SINGULARITY_IMAGE}
-    entrypoint: ["/bin/bash"]
+    entrypoint: [""]
   stage: deploy
   interruptible: true
   rules: